1. Field of the Invention
The present invention relates to a mold to be used for manufacturing a pneumatic tire. In detail, the present invention relates to an improvement of a bead ring of the mold.
2. Description of the Related Art
A two phase mold is used at a step of vulcanizing a pneumatic tire. FIG. 9 is a sectional view showing a part of a conventional two phase mold 2 together with a green tire G and a bladder B. The two phase mold 2 comprises a tread segment 4, a side plate 6 and a bead ring 8. The bead ring 8 includes an inner peripheral surface 10 and a bottom forming surface 12. At the vulcanizing step, first of all, the green tire G formed previously is put into the opened mold 2. Next, the mold 2 is closed. Then, the bladder B is filled with a high-temperature gas. The bladder B expands along the inner peripheral surface 10 and a cavity is formed by the mold 2 and the bladder B. The green tire G is simultaneously pressurized and heated in the cavity. By the pressurization and the heating, a rubber composition flows. A rubber causes a crosslinking reaction by the heating so that a tire is obtained. A bead is formed by the bead ring 8 and the bladder B. Such a mold 2 has been disclosed in U.S. Pat. No. 6,398,533 (Japanese Laid-Open Patent Publication No. 2001-9840).
In some cases, an end E of the green tire G is caught on a boundary 16 between the inner peripheral surface 10 and the bottom forming surface 12 as shown in FIG. 10 when the green tire G is put into the mold 2. By the expansion of the bladder B, the end E is pushed outward in an axial direction as shown in an arrow A1 and is moved toward the bottom forming surface 12. At this time, the rubber composition is interposed between the bladder B and the inner peripheral surface 10 in some cases. The rubber composition is interposed so that a tongue-shaped portion To is formed on a toe side of a bead Be as shown in FIG. 11. This phenomenon is referred to as a “long toe”. In case of a tire comprising a rubber chafer (a chafer in which a fabric is not used), a rubber composition flows more easily than a tire comprising a canvas chafer (a chafer formed by a fabric impregnated with a rubber). For this reason, the tongue-shaped portion To is formed easily. The tongue-shaped portion To deteriorates an appearance and quality of the tire. The tongue-shaped portion To having a large dimension is to be removed. A removing work is carried out manually by using a knife. For the removing work, a great deal of time and labor is required.
If a thickness of the end E of the green tire G is set to be small, the generation of the tongue-shaped portion To can be suppressed. In some cases, however, an insufficiency of a volume of the bead Be is generated by the thin end E. This phenomenon is referred to as a “smash”. In the tire having the smash generated thereon, an air seal of a bead and a rim is not sufficient. In the tire, the thickness of the bead is insufficient. For this reason, there is also a possibility that the bead might be damaged when the tire is incorporated into the rim. In the tire, furthermore, a position of a bead core for each section is varied. The variation inhibits a uniformity of the tire. The same problem is also generated in a tire obtained by a two piece mold. It is an object of the present invention to provide a mold by which a tire of high quality can be obtained.